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plan-view and cross-sectional configuration. To
minimize the error in estimating the carier
recombination efficiency at defect sites, linescan
measurements were performed. However, it must be
cautioned here that the effect of snures topography
could not be eliminated. Fig. 5 shows a CL
linescan across an as-deposited CdTe film revealing
avery high degree of non-radiative recombination at
grainboundaries and at intragrain defects. Fig. 6 is
a similar CL linescan on the same sample afer
CdC12 treatment. This indicates a factor of two
reduction in the recombination efficiency at grain
boundaries and at intragmin defects. This is clearly
indicative of the passivating effect of the CdC12
Figure 5: CL linescan superimposed on an SEM
image of an as-deposited CdTe film.
Figure 6: CL linescan superimposed on an SEM
image of the CdTe film shown in Fig. 5 aflr
All CdS films examined in this study exhibited
pinholes and discontimiities varying in size and
density. This could have a significant impact on
cell performance, as these pinholes could provide
shnting paths between the CdTe and the SnO2.
The CdS grains are heavily faulted, with a high
density of staging faults. This will have a
deleterious effect on the CdS/CdTe interface region,
as we have shown in a previous study that planar
defects in CdS tend to propagate into the CdTe
films. Most CdWe grains are heavily faulted, with a
high density of dislocations, stacking faults and
twins. The defect density varied from one grain to
another. However, the density is not significantly
affectedby substrate temperature. Hence, the widely
observed improvement in device performance with
increasing substrate temperature is not caused by a
reduction in structural defect density.
This study clearly revealed that grain boundaries
and intragramin defects in CdTe act as active non-
radiative recombination sites. CL examination
showed that CdC12 treatment markedly lowers the
recombination efficierry of grain boundaries, and
intragrain defects in CdTe.
At deposition temperatures below 450*C, only
small amounts (~-1%) of sulfur were detected in the
CdTe films in the vicinity of the interface. In CdTe
films deposited at 6250C, on the other hand, sulfur
levels exceeding 10% were detected. This clearly
indicates that CdTe devices deposited at high
temperatures have an alloyed (CdSXTe1 x) active
This work was performed for the U.S. Department
of Energy under contract No. DE-AC36-
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NCPV preprints for the 2. world conference on photovoltaic solar energy conversion, article, September 1, 1998; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc707815/m1/41/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.